Methods of recovering reusable fibers

ABSTRACT

Methods of recovering reusable fibers from mixtures of waste fibers and/or fabrics and synthetic, cross-linked polyacrylate resins which comprise: (1) heating a mixture of waste fibers and/or fabrics and synthetic, cross-linked polyacrylate resins in an aqueous saponifying solution containing an alkali metal hydroxide and a water-soluble salt containing a monovalent cation, which solution saponifies the synthetic, cross-linked polyacrylate resins and initiates their decomposition or solubilization without undesirably swelling the same; (2) treating the mixture of waste fibers and/or fabrics and synthetic, cross-linked, saponified, polyacrylate resins in an aqueous washing solution containing a water-soluble salt containing a monovalent cation to remove alkali therefrom; and (3) washing and recovering the reusable fibers from the mixture of waste fibers and/or fabrics and decomposed or solubilized synthetic, cross-linked polyacrylate resins.

Drelich et a1.

States 1 1 METHODS OF RECOVERING REUSABLE FIBERS [73] Assignee:

[22] Filed:

Johnson & Johnson, New

Brunswick, NJ.

June 29, 1973 [21] App]. No.: 375,216

[52] 11.8. C1 162/8, 8/141, 16 2/60 [51] Int. Cl. D21c 5/02 [58] Field of Search 162/6, 7, 8, 4, 60; 8/137.5, 141

[56] References Cited UNITED STATES PATENTS 1,555,674 9/1925 Kellner 162/6 2,116,511 5/1938 Earle 162/6 X 2,690,375 9/1954 Brown et a1. 8/1375 X 2,936,211 5/1960 Kocay et a1 8/1375 X 2,959,513 11/1960 Savage 162/6 3,262,838 7/1966 Vieth et a1. 162/8 3,597,148 8/1971 Carroll et a1 8/1375 3,620,909 11/1971 Gleason 162/8 3,766,001 10/1973 Gleason et a1. 162/8 [451 Mar. 25, 1975 3,816,238 6/1974 Mitchell 162/8 FOREIGN PATENTS OR APPLICATIONS 1,459,072 1965 France 8/l37.5

Primary Examiner-S. Leon Bashore Assistant Examiner-Alfred DAndrea, Jr.

[57] ABSTRACT Methods of recovering reusable fibers from mixtures of waste fibers and/0r fabrics and synthetic, crosslinked polyacrylate resins which comprise: (1) heating a mixture of waste fibers and/or fabrics and synthetic, cross-linked polyacrylate resins in an aqueous saponifying solution containing an alkali metal hydroxide and a water-soluble salt containing a monovalent cation, which solution saponifies the synthetic, crosslinked polyacrylate resins and initiates their decomposition or solubilization without undesirably swelling the same; (2) treating the mixture of waste fibers and- /or fabrics and synthetic, cross-linked, saponified, polyacrylate resins in an aqueous washing solution containing a water-soluble salt containing a monovalent cation to remove alkali therefrom; and (3) washing and recovering the reusable fibers from the mixture of waste fibers and/or fabrics and decomposed or solubilized synthetic, cross-linked polyacrylate resins.

21 Claims, 1 Drawing Figure has/0mg, Sap/424mm; 4m:

PECal EE/A G n/E 25115451.: H5528 Maswwq 0 7/ 42/21/75 40/0 ,saaur/m/ PATENIEBmzsms 3.873.411

Ms/m/q, SEPAeAT/N 4N0 1 METHODS OF RECOVERING REUSABLE FIBERS BACKGROUND OF THE INVENTION In various industries such as the textile, leather, paper, paper products, and like industries, there is a need to recover fibers which have been coated or impregnated with resins. This need to recover fibers and recycle them grows increasingly important with the ever growing awareness of our basic ecological requirements.

In the following specification, the present invention will be described in particularity with reference to the recovery of fibers used in the manufacture of woven, knitted, felted, and especially nonwoven fabrics in the textile industry. This, however, is merely illustrative and the broader aspects of the inventive concept are not to be construed as limited thereto.

One of the conventional commercial methods of making nonwoven fabrics is to prepare a relatively flat, fibrous web of several thicknesses or layers of fibers which are arranged generally in parallel or carded fashion, or distributed in random or haphazard array.

These fibrous layers are then bonded, either in overall fashion or in intermittent print patterns, with an adhesive bonding agent or a synthetic resin, to form an integral, self-sustaining nonwoven fabric. At the end of the manufacturing operation, the nonwoven fabric is usually trimmed to a desired predetermined width, thus creating two relatively narrow edge strips of trim waste." These strips of trim waste represent only a small proportion of the total finished nonwoven fabric, but ultimately accumulate to very considerable amounts and are well worth recovering and recycling, not only from an ecological viewpoint but also for economic reasons.

Additionally, on occasion, the body of the nonwoven fabric is found unsatisfactory and is discarded to also become waste. Such waste, often termed -flat waste, also accumulates to very large amounts in relatively very short periods of time. And, of course, there are also odds and ends of miscellaneous nonwoven fabrics which become waste for various reasons.

One very large class of synthetic resins used for bonding nonwoven fabrics comprises the polymers and copolymers of vinyl esters, of which polyvinyl acetate is presently the most important single member. Fortunately, these polyvinyl ester resins are susceptible to decomposition, solubilization, or saponification treatments with caustic and the fibers bonded thereby are recoverable by known methods.

Another large class of synthetic resins used for bonding nonwoven fabrics comprises the polymers and copolymers of vinyl halides, of which polyvinyl chloride is presently the most important single member. Fortunately, these polyvinyl chloride resins are susceptible to decomposition, solubilization, or saponification treatments with caustic and added ketones or alcohols (see US. Pat. No. 2,832,633 which issued Apr. 29, 1958) and the fibers bonded thereby are also recoverable.

In recent years, however, another class of synthetic resins have become very important commercially for bonding nonwoven fabrics. These resins are the selfcross-linkable polyacrylate resins which, unfortunately, are not susceptible to decomposition or solubilization recovery treatments, either with caustic alone or with caustic and added chemicals such as ketones, alcohols, lactones, or sulfoxides.

Specifically, when nonwoven fabric trim waste, flat waste, or other waste too, for that matter, which has been bonded with a well-cured, self-cross-linking polyacrylate resin is boiled under pressure at elevated temperatures in dilute caustic alone or in a dilute caustic-ketone, alcohol, lactone, or sulfoxide solution for a long period of time, the resin is attacked to some degree but is not completely decomposed or made soluble. The resin does break down to a sufficient degree but the resulting product is a swollen, viscous, slimy jelly which clings tenaciously to the fibers and does not wash out. If dried, the jelly-covered fibers become a tightly bonded, unworkable, stiff mass of fibers and res1n.

Such difficulties have been avoided to some extent more recently by methods involving an additional treatment of the waste fibers and polyacrylate resins with a neutral or alkaline oxidizing agent, such as hydrogen peroxide. Such methods are described more fully in copending patent applications Ser. Nos; 285,388, now US. Pat. No. 3,801,273 and 285,389 now US. Pat. No. 3,843,321, filed Aug. ,30, 1972. Unfortunately, such methods, although generally satisfactory and commercially acceptable, have been found to somewhat degrade many waste fibers to some degree and even further improved methods are therefore desired.

It is therefore a principal purpose of the present invention to provide methods of recovering reusable fibers from mixtures of waste fibers and synthetic, crosslinked polyacrylate resins without degrading the fibers to a degree whereby their usefulness for recycling and reuse in textile or other processes for the production of fabrics or other fibrous products is not impaired.

STATEMENT OF THE INVENTION It has been discovered that such principal purpose and other purposes to be described hereinafter can be accomplished by heating the mixture of waste fibers and synthetic, cross-linked polyacrylate resins within the range of from about C. to about C. for a period of time of from about A hour to about 2 hours in an aqueous saponifying solution containing from about 1% by weight to about 5% by weight of an alkali metal hydroxide and from about 1% by weight to about 7% by weight of a water-soluble salt containing a monovalent cation to saponify and initiate the decomposition or solubilization of the synthetic, cross-linked polyacrylate resin without undesirably swelling, the same; washing the waste fibers and the synthetic, crosslinked polyacrylate resin in an aqueous solution containing from about 1% by weight to about 7% by weight of a water-soluble salt containing a monovalent cation; and washing, separating and recovering the reusable fibers from the mixture of waste fibers and decomposed or solubilized synthetic, cross-linked polyacrylate resins.

GENERAL DESCRIPTION OF THE INVENTION In the following specification, there are described preferred embodiments of the invention, but is is to be understood that the inventive concept is not to be considered limited to the specific embodiments disclosed except as detennined by the scope of the appended claims.

TI-IE FIBERS The reusable fibers which form the recoverable materials of the present inventive concept are primarily of cellulosic nature, such as cotton or rayon (viscose or regenerated cellulose). Other fibers, however which are capable of resisting the chemical treatments described herein, without undesirable or excessive degradation, decomposition, or solubilization, may also be applicable. Examples of such other applicable fibers include: nylon polyamide 6/6 and 6; the polyolefins such as polyethylene and polypropylene; polyesters; formalized, insoluble polyvinyl alcohol; etc.

THE RESINS The synthetic cross-linked polyacrylate resin which is to be separated and removed from the fibers may be one or more of a relatively large group of synthetic resins well known in industry and may be of an internally, self-cross-linking type or an externally cross-linking type. Specific examples of such synthetic cross-linkable resins include: (1) polymers and copolymers of the acrylic resins such as ethyl acrylate, methyl acrylate, butyl acrylate, ethyl butyl acrylate, ethyl hexyl acrylate, hydroxyethyl acrylate, dimethyl amino ethyl acrylate, etc; (2) polymers and copolymers of the methacrylic resins such as methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, butyl methacrylate, etc.; (3) copolymers of such acrylates and methacrylates and other copolymerizable materials such as vinyl acetate, vinyl chloride, vinylidene chloride, styrene, itaconic acid, acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, acrylamide, N-isopropyl acrylamide, N- methylol acrylamide, methacrylamide, etc.

These resins may be present either as homopolymers comprising a single repeating monomeric unit, or they may be used as copolymers comprising two, three, or more different monomeric units which are arranged in random fashion, or in a definite ordered alternating fashion, within the polymer chain. Also included within the inventive concept are the block polymers comprising relatively long blocks of different monomeric units in a polymer chain and graft polymers comprising chains of one monomer attached to the backbone of another polymer chain.

THE HEATING STEP The mixture of the waste fibers and the synthetic cross-linked polyacrylate resins is heated or cooked with or without pressure at elevated temperatures within the range of from about 85 C. (with or without pressure) to about 150 C. (with pressure) for a period of from about A hour to about 2 hours in an aqueous treating solution containing from about 1% by weight to about 5% by weight of an alkali metal hydroxide and from about 1% by weight to about 7% by weight of a water-soluble monovalent metal salt. These temperatures, pressures, and times are mutually interdependent and interrelated, and can be varied as is normally done in conventional chemical reactions and treatments.

THE ALKALl METAL HYDROXIDE The alkali metal hydroxide is preferably sodium hydroxide or potassium hydroxide but the hydroxides of other alkali metals such as lithium, etc. are also suitable.

As indicated previously, the concentration of the alkali metal hydroxide in the heating solution ranges from about 1% by weight to about 5% by weight. Lower or higher concentrations may be used but often lead to too slow or too rapid reactions or possible damage to the waste fibers and are not as desirable under ordinary circumstances.

THE WATER-SOLUBLE SALT CONTAlNlNG A MONOVALENT CATION The water-soluble salt containing a monovalent cation may be selected from a relatively large group of salts including sodium chloride, potassium chloride, lithium chloride, ammonium chloride, sodium bromide, sodium carbonate, sodium sulfate, potassium sulfate, sodium nitrate, sodium bicarbonate, sodium phosphate, sodium borate, potassium nitrate, etc. It is merely necessary that the cations produced in solution be monovalent; that the salts be sufficiently watersoluble; and that they possess sufficient stability and do not decompose during the heating or cooking step at elevated temperatures.

As indicated previously, the concentration of the water-soluble monovalent metal salt in the heating solution ranges from about 1% to about 7% by weight. Lower percentages are not desired but higher percentages may be used but are normally not efficient or economical.

THE HEATING STEP During the heating at an elevated temperature, as describedherein, the synthetic, cross-linked polyacrylate resins are saponified and their decomposition or solubilization is initiated. Also, during this time, the resin is attacked and is partially broken down or decomposed, or made soluble. Fortunately, however, the resins do not swell to previously-experienced levels and they do not become as slimy or jelly-like, nor do they cling quite as tenaciously to the waste fibers. As a result of such decreased swelling and lessened gelation, the subsequent recovery steps are made much simpler.

THE WASHlNG STEP Subsequent to the heating at the elevated tempera ture, as described herein, at which point the pH may be in the range of about 13 or 14, the reaction product is washed with an aqueous washing solution containing from about 1% by weight to about 7% by weight of a water-soluble monovalent metal salt but in any event at a concentration not less than the salt concentration used during the heating or cooking step. The concentration of the salt in the washing solution must be kept at a level at least equal to about 1% by weight and must not be allowed to fall under such a minimum, critical value. However, the concentration of the salt in the washing solution may be permitted to be above the 7% value but such is deemed uneconomical and unneces sary under normal circumstances.

The mixture of waste fibers and resin materials is washed with the monovalent metal salt wash solution several times, during which time the alkali from the original alkali metal hydroxide is washed out and the pH is gradually reduced. Some or all of the sodium polyacrylate resin materials formed as a result of the saponification is also removed at this time. Other constituents, contaminants, and miscellaneous by-products are also washed out at the same time. The pH of the cooking solution which originally was as high as about 13 or 14 decreases to about 10 or 9 or even lower during the washings.

After several salt washings of the mixture of fibers and polyacrylate resin and concomitant reduction of the pH, then washing with water .or a very dilute alkali, such an ammonia, is in order to remove any remaining polyacrylate resin materials to separate and recover the reusable fibers in a form suitable for recycling and reuse in textile or related processes.

ALTERNATIVE WASHING PROCEDURES The washing with the monovalent metal salt solution must be very thorough and several washings are required. The number of washings in some stubborn cases has been found to be as many as fifteen which, of course, is undesirable from a commercial or economic viewpoint. The number of washings, however, may be reduced by the following alternative procedures.

DILUTE ACID WASHING After one or two washings of the mixture of fibers and polyacrylate resin with the water-soluble monovalent metal salt solution, washing with a dilute acid converts the polyacrylate resin from the sodium salt form to the acid form and deswells and shrinks down the size of the mixture of fibers and polyacrylate resin. This deswells the polyacrylate resin, allowing better penetration and circulation of the wash liquors through the mixture, and thus reduces the total number of washings required. Any suitable diluted acid may be used such as dilute hydrochloric, sulfuric, nitric, phosphoric, acetic, butyric, chloracetic, chlorpropionic, citric, formic, fumaric, iodic, isobutyric, lactic, maleic, malic, malonic, mandelic, naphthoic, nitrous, oxalic, periodic, phosphorous, phthalic, picric, propionic, pyrophosphoric, salicylic, succinic, sulfanilic, sulfurous, tartaric, and like acids. These acids are used in diluted form and are normally used in concentrations of from about 3% to about or less. It is to be noted that these acids have ionization or dissociation constants equal to or greater than that of polyacrylic acid, which is about I X l0- at 25 C.

POLYVALENT SALT WASHING After one or two washings of the mixture of fibers and polyacrylate resins with the water-soluble monovalent metal salt solution, washing with a water-soluble polyvalent metal salt solution similarly deswells and shrinks down the size of the mixture of fibers and polyacrylate resin. This also reduces the total number of washings required. Any suitable water-soluble-polyvalent metal salt of calcium, magnesium, zinc, aluminum, iron, chromium, cobalt, nickel, copper, etc., may be used in the form of the chloride, sulfate, nitrate, phosphate, acetate, etc., provided they are sufficiently water-soluble and stable under the conditions used.

These polyvalent metal salts are used in concentrations of from about 0.05% to about 2% by weight or even slightly higher.

The various steps and combinations thereof pertaining to the methods of the present inventive concept are set forth in THE FIGURE of the drawing which accompanies the specification.

The invention will be further illustrated in greater detail by the following specific examples. It should be understood, however, that, although these examples may describe in particular detail some of the more specific features of the invention, they are given primarily for purposes of illustration and the invention in its broader aspect is not to be construed as limited thereto.

EXAMPLE 1 One hundred grams of rayon trim waste fibers produced in the course of the manufacture of nonwoven fabric comprising several layers of card webs and containing as a bonding agent approximately 20% (20 grams) of synthetic, cross-linked polyethylacrylate is introduced into a vessel containing 700 grams of water, 21 grams of sodium hydroxide, and 21 grams of sodium chloride. This mixture of trim waste fibers with polyethylacrylate and alkaline reagents is heated under pressure for a period of one hour at a temperature of l25C.-The polyethylacrylate is attacked during this heating step. At the completion of this cooking operation and after appropriate cooling in air, the fiber mass is examined and found to feel slippery but not covered with an appreciable amount of viscous, slimy gel.

The mass of cooked trim waste fibers with the decomposition products of polyethylacrylate therein is then squeezed down to a liquor: fiber ratio of about 2 /2 to 1. The fiber-resin mass is subjected to two more separate rinses and squeezings, each rinse containing 700 grams of water in which there is dissolved 21 grams of sodium chloride. During these rinses in the sodium chloride solution, the fiber mass swells slightly, most of the sodium hydroxide is removed, and a considerable portion of the acrylic decomposition products are also removed. At no time, does the fiber mass swell measurably greater than its volume at the completion of the cook. The pH of the fiber mass is approximately 9 and the sodium hydroxide content is well below The rinsed and squeezed fiber mass is introduced into a solution containing 3 /2 grams glacial acetic acid and 21 grams sodium chloride dissolved in 700 milliliters of water /2% acetic acid solution). The slippery, slimy feeling in the mass is greatly diminished, but the fibrous mass does not shrink greatly and still more of the acrylic decomposition products are dissolved in the excess liquid. This mat is squeezed again down to a liquor: fiber ratio of about 2 /2 to l, thereby removing still more of the acrylic decomposition products and other by-products of the reaction.

The fibrous mat is once again rinsed and squeezed in a salt solution (700 grams water and 21 grams sodium chloride), thereby removing still more of the undesired acrylic decomposition products. The pH of the mat at this point is approximately 5.

The fibrous mat is now rinsed and squeezed in two consecutive operations, each in 700 milliliters of water containing 8 milliliters of commercial aqua ammonia (containing 28% NH;,). During the rinses the fiber mat again becomes slippery to the touch and reswells slightly but not more than the swelling encountered at the end of the alkaline cooking operation. During these rinses and squeezings, the acrylic decomposition products are further removed from the fibrous mat leaving now only a relatively small portion among the fibers.

The fibers are then washed in an excess of running warm water (about to ll0F.). further removing the acrylic by-products. The fibers are squeezed to remove excess water and as much undesirable byproducts as possible. Finally. the fiber mass is washed well in relatively hot water, about F. for a period of 5 minutes with fresh hot water being introduced during this time. At the completion of this wash, the pH of the fiber mass is approximately neutral. After the fibers are dried in an oven, it is seen that they are fluffy and essentially completely free of all acrylic residues and other undesirable by-products and are quite suitable for reuse in textile processes for the production of nonwoven, woven or knitted fabrics.

EXAMPLE II The procedures of Example I are followed substantially as set forth therein except that sodium sulfate is used instead of sodium chloride in the saponification step and in the washing step. The results are generally comparable to those obtained in Example I and the recovered fibers are suitable for use in textile operations.

EXAMPLE III The procedures of Example I are followed substantially as set forth therein except that sodium bisulfate is used instead of sodium chloride in the saponification step and in the washing step. The results are generally comparable to those obtained in Example I and the recovered fibers are suitable for use in textile operations.

EXAMPLE IV The procedures of Example I are followed substantially as set forth therein except that ammonium chloride is used instead of sodium chloride in the saponification step and in the washing step. The results are generally comparable to those obtained in Example I and the recovered fibers are suitable for use in textile operations.

EXAMPLE V The procedures of Example I are followed substantially as set forth therein except thatsodium carbonate is used instead of sodium chloride in the saponification step and in the washing step. The results are generally comparable to those obtained in Example I and the recovered fibers are suitable for use in textile operations.

EXAMPLE VI The proceduresof Example I are followed substantially as set forth therein except that sodium bicarbonate is used instead of sodium chloride in the saponification step and in the washing step. The results are generally comparable to those obtained in Example I and the recovered fibers are suitable for use in textile operations.

EXAMPLE VII The procedures of Example I are followed substantially as set forth therein except that potassium chloride is used instead of sodium chloride in the saponification step and in the washing step. The results are generally comparable to those obtained in Example I and the recovered fibers are suitable for use in textile operations.

EXAMPLE VIII The procedures of Example I are followed substantially as set forth therein except that the saponification step is carried out at 100C. in a vessel open to the atmosphere for I% hours. The results are generally comparable to those obtained in Example I and the recovered fibers are suitable for use in textile operations.

EXAMPLE IX The procedures of Example I are followed substantially as set forth therein except that the concentration of sodium hydroxide in the saponification step is increased from 3% to 4 /2%. The results are generally comparable to those obtained in Example I and the recovered fibers are suitable for use in textile operations.

EXAMPLE X The procedures of Example I are followed substantially as set forth therein except that the concentration of sodium hydroxide in the saponification step is decreased from 3% to 2%. The results are generally comparable to those obtained in Example I and the recovered fibers are suitable for use in textile operations.

EXAMPLE XI The procedures of Example I are followed substantially as set forth therein except that the concentration of the sodium chloride used in the various operations is decreased from 3% to 1% (7 grams per 700 milliliters of water). The results are generally comparable to those obtained in Example I and the recovered fibers are suitable for use in textile operations.

EXAMPLE XII The procedures of Example I are followed substantially as set forth therein except that the concentration of the sodium chloride used in the various operations is increased from 3% to 7% (49 grams per 700 milliliters of water). The results are generally comparable to those obtained in Example I and the recovered fibers are suitable for use in textile operations.

EXAMPLE XIII The procedures of Example I are followed substantially as set forth therein except that only 50 grams of rayon trim waste fibers are used instead of 100 grams. The results are generally comparable to those obtained in Example I and the recovered fibers are suitable for use in textile operations.

EXAMPLE XIV The procedures of Example I are followed substantially as set forth therein except that. only grams of rayon trim waste fibers are used instead of grams. The results are generally comparable to those obtained in Example I and the recovered fibers are suitable for use in textile operations.

EXAMPLE XV The procedures of Example I are followed substantially as set forth therein except that only 25 grams of rayon trim waste fibers are used instead of I00 grams. The results are generally comparable to those obtained in Example I and the recovered fibers are suitable for use in textile operations.

EXAMPLE XVI those obtained in Example I and the recovered fibers are suitable for use in textile operations.

EXAMPLE XVll The procedures of Example XVI are followed substantially as set forth therein except that a 0.25% solution of calcium chloride is substituted for /2% zinc chloride solution. A further change is made in this Example in the rinsing immediately following the two dilute ammonia rinses. In this Example, the mat is rinsed with 0.75% acetic acid solution (700 ml) to remove any calcium salts remaining. The last traces of acrylic decomposition products are removed by rinses, first in warm and finally in hot water. The results are generally comparable to those obtained in Example XVI and the recovered fibers are suitable for use in textile operations.

EXAMPLE XVlll The procedures of Example I are followed substantially as set forth therein except that a /2% solution of formic acid is substituted for the /2% solution of acetic acid. The results are generally comparable to those obtained in Example I and the recovered fibers are suitable for use in textile operations.

EXAMPLE XIX The procedures of Example I are followed substantially as set forth therein except that a /2% solution of citric acid is substantially for the /2% solution of acetic acid. The results are generally comparable to those obtained in Example 1 and the recovered fibers are suitable for use in textile operations.

EXAMPLE XX One hundred grams of rayon trim waste fibers produced in the course of the manufacture of nonwoven fabric comprising several layers of card webs and containing as a bonding agent approximately 20% (20 grams) of synthetic, cross-linked polyethylacrylate is introduced into a vessel containing 700 grams of water, 21 grams of sodium hydroxide, and 21 grams of sodium chloride. This mixture of trim waste fibers with polyethylacrylate and alkaline reagents is heated under pressure for a period of 1 hour at a temperature of 125C. The polyethylacrylate is attacked during this heating step. At the completion of this cooking operation and after appropriate cooling in air, the fiber mass is examined and found to feel slippery but not covered with an appreciable amount of viscous, slimy gel.

The mass of cooked trim waste fibers with the decomposition products of polyethylacrylate therein is then squeezed down to a liquor: fiber ratio of about 2 /2 to l. The fiber-resin mass is subjected to eight more separate rinses and squeezings, each rinse containing 700 grams of water in which there is dissolved 21 grams of sodium chloride. During these rinses in the sodium chloride solution, the fiber mass swells slightly, most of the sodium hydroxide is removed, and a considerable portion of the acrylic decomposition products are also removed. At no time, does the fiber mass swell measurably greater than its volume at the completion of the alkaline saponification cook. The sodium hydroxide content is essentially negligible.

The fibers are then washed in an excess of running warm water (about 100 to 1 F removing substantially the last traces of the acrylic by-products. The fibers are squeezed to remove excess water and any undesirable by-products which may remain. Finally, the fiber mass is washed well in relatively hot water, about F., for a period of 5 minutes with fresh hot water being introduced during this time. At the completion of this wash, the pH of the fiber mass is approximately neutral. After the fibers are dried in an oven, it is seen that they are fluffy and essentially completely free of all acrylic residues and other undesirable by-products and are quite suitable for reuse in textile processes for the production of nonwoven, woven or knitted fabrics.

EXAMPLE XXI The procedures of Example XVl are followed substantially as set forth therein except that a 1% solution of zinc chloride is substituted for the /2% acetic acid solution. As soon as the fibers are introduced to the dilute zinc chloride solution, the slimy and slippery feel immediately disappears. The subsequent rinsing in dilute ammonium hydroxide causes the formation of a zinc ammine complex which gradually washes out the zinc at the same time that it washes out the deleterious by-products. The results are generally comparable to those obtained in Example XVI and the recovered fibers are suitable for use in textile operations EXAMPLE XXlI The procedures of Example XVll are followed substantially as set forth therein except that a 0.10% solution of calcium chloride is substituted for /2% zinc chloride solution. A further change is made in this Example in the rinsing immediately following the two dilute ammonia rinses. In this Example, the mat is rinsed with 0.75% acetic acid solution (700 ml) to remove any calcium salts remaining. The last traces of acrylic decomposition products are removed by rinses, first in warm and finally in hot water. The results are generally comparable to those obtained in Example XVll and the recovered fibers are suitable for use in textile operations.

EXAMPLE XXlll The procedures of Example XVII are followed substantially as setforth therein except that a 0.50% solution of calcium chloride is substituted for /2% zinc chloride solution. A further change is made in this Example in the rinsing immediately following the two dilute ammonia rinses. In this Example, the mat is rinsed with 0.75% acetic acid solution (700 ml) to remove any calcium salts remaining. The last traces of acrylic decomposition products are removed by rinses, first in warm and finally in hot water. The results are generally comparable to those obtained in Example XVI] and the recovered fibers are suitable for use in textile operations.

Although several specific examples of the inventive concept have been described. the same should not be construed as limited thereby nor to the specific features mentioned therein but to include various other equivalent features as set forth in the claims appended hereto. It is understood that any suitable changes, modifications and variations may be made without departing from the spirit and scope of the invention.

What is claimed is:

1. A method of recovering reusable fibers from mixtures of waste fibers and synthetic, cross-linked polyacrylate resins which comprises: heating at temperatures within the range of from about 85C. to about 150C. for from about A hour to about 2 hours, a mixture of waste fibers and synthetic, cross-linked polyacrylate resins in an aqueous saponifying solution containing from about 1% by weight to about 5% by weight of an alkali metal hydroxide and from about 1% by weight to about 7% by weight of a water-soluble salt containing a monovalent cation which solution saponifies the synthetic, cross-linked polyacrylate resins and initiates their decomposition or solubilization without undesirably swelling the same; treating the mixture of waste fibers and synthetic, cross-linked, saponified, polyacrylate resins in an aqueous washing solution containing at least about 1% by weight of a water-soluble salt containing a monovalent cation to remove alkali therefrom; and recovering the reusable fibers from the mixture of waste fibers and decomposed or solubilized synthetic, cross-linked polyacrylate resins.

2. A method as defined in claim 1 wherein the watersoluble salt in the saponifying solution is sodium chloride.

3. A method as defined in claim 1 wherein the watersoluble salt in the saponifying solution is sodium sulfate.

4. A method as defined in claim 1 wherein the watersoluble salt in the saponifying solution is sodium bisulfate.

5. A method as defined in claim 1 wherein the watersoluble salt in the saponifying solution is sodium carbonate.

6. A method as defined in claim 1 wherein the watersoluble salt in the saponifying solution is ammonium chloride.

7. A method as defined in claim 1 wherein the watersoluble salt in the saponifying solution is potassium chloride.

8. A method as defined in claim 1 wherein the watersoluble salt in the aqueous washing solution is sodium chloride.

9. A method as defined in claim 1 wherein the watersoluble salt in the aqueous washing solution is sodium sulfate.

10. A method as defined in claim 1 wherein the water-soluble salt in the aqueous washing solution is sodium bisulfate.

11. A method as defined in claim 1 wherein the water-soluble salt in the aqueous washing solution is so dium carbonate.

12. A method as defined in claim 1 wherein the water-soluble salt in the aqueous washing solution is ammonium chloride.

13. A method as defined in claim 1 wherein the water-soluble salt in the aqueous washing solution is potassium chloride.

14. A method as defined in claim 1 wherein there is a second washing treatment with a solution of a salt containing a polyvalent metal cation, said salt being present in the solution in amounts of from about 0.05% to about 2% by weight.

15. A method as defined in claim 14 wherein the polyvalent metal is zinc chloride.

16. A method as defined in claim 14 wherein the polyvalent metal salt is calcium chloride.

17. A method as defined in claim 1 wherein there is a second washing treatment with a dilute acid having a dissociation constant of at least about 1 X 10', said acid being employed in concentrations of from about /2% to about 3%.

18. A method as defined in claim 17 wherein the dilute acid is acetic acid.

19. A method as defined in claim 17 wherein the dilute acid is formic acid.

2.0. A method as defined in claim 17 wherein the dilute acid is citric acid.

21. A method of recovering reusable fibers from mixtures of waste fibers and synthetic, cross-linked poly acrylate resins which comprises: heating a mixture of waste fibers and synthetic, cross-linked polyacrylate resins within the range of from about C. to about C. for a period of from about V2 hour to about 2 hours in an aqueous saponifying solution containing from about 1% by weight to about 5% by weight of an alkali metal hydroxide and from about 1% by weight to about 7% by weight of a water-soluble salt containing a monovalent cation, which solution saponifies the synthetic, cross-linked polyacrylate resins and initiates their decomposition or solubilization without undesirably swelling the same; treating the mixture of waste fibers and synthetic, cross-linked, saponified, polyacrylate resins in an aqueous washing solution containing from about 1% by weight to about 7% by weight of a water-soluble salt containing a monovalent cation to remove alkali therefrom; and recovering the reusable fibers from the mixture of waste fibers and decomposed or solubilized synthetic, cross-linked polyacrylate res 

1. A METHOD OF RECOVERING REUSABLE FIBERS FROM MIXTURES OF WASTE FIBERS AND SYNTHETIC, CROSS-LINKED POLYACRYLATE RESINS WHICH COMPRISES: HEATING AT TEMPERATURES WITHIN THE RANGE OF FROM ABOUT 85*C. TO ABOUT 150*C. FOR FROM ABOUT 1/4 HOUR TO ABOUT 2 HOURS, A MIXTURE OF WASTE FIBERS AND SYNTHETIC, CROSSLINKED POLYACRYLATE RESINS IN AN AQUEOUS SAPONIFYING SOLUTION CONTAINING FROM ABOUT 1% BY WEIGHT TO ABIUT 5% BY WEIGHT OF AN ALKALI METAL HYDROXIDE AND FROM ABOUT 1% BY WEIGHT TO ABOUT 7% BY WEIGHT OF A WATER-SOLUBLE SALT CONTAINING A MONOVALENT CATION WHICH SOLUTION SAPONIFIES THE SYNTHETIC, CROSSLINKED POLYACRYLATE RESINS AND INITIATES THEIR DECOMPOSITION OR SOLUBILIZATION WITHOUT UNDESIRABLY WITHOUT SWELLING THE SAME; TRE ATING THE MIXTURE OF WASTE FIBERS AND SYNTHETIC, CROSS-LINKED, SAPONIFIED, POLYACRYLATE RESINS IN AN AQOUS WASHING SOLUTION CONTAINING AT LEAST ABOUT 1% BY WEIGHT OF A WATER-SOLUBLE SALT CONTAINING A MONOVALENT CATION TO REMOVE ALKALI THEREFROM; AND RECOVERING THE REUSABLE FIBERS FROM THE MIXTURE OF WASTE
 2. A method as defined in claim 1 wherein the water-soluble salt in the saponifying solution is sodium chloride.
 3. A method as defined in claim 1 wherein the water-soluble salt in the saponifying solution is sodium sulfate.
 4. A method as defined in claim 1 wherein the water-soluble salt in the saponifying solution is sodium bisulfate.
 5. A method as defined in claim 1 wherein the water-soluble salT in the saponifying solution is sodium carbonate.
 6. A method as defined in claim 1 wherein the water-soluble salt in the saponifying solution is ammonium chloride.
 7. A method as defined in claim 1 wherein the water-soluble salt in the saponifying solution is potassium chloride.
 8. A method as defined in claim 1 wherein the water-soluble salt in the aqueous washing solution is sodium chloride.
 9. A method as defined in claim 1 wherein the water-soluble salt in the aqueous washing solution is sodium sulfate.
 10. A method as defined in claim 1 wherein the water-soluble salt in the aqueous washing solution is sodium bisulfate.
 11. A method as defined in claim 1 wherein the water-soluble salt in the aqueous washing solution is sodium carbonate.
 12. A method as defined in claim 1 wherein the water-soluble salt in the aqueous washing solution is ammonium chloride.
 13. A method as defined in claim 1 wherein the water-soluble salt in the aqueous washing solution is potassium chloride.
 14. A method as defined in claim 1 wherein there is a second washing treatment with a solution of a salt containing a polyvalent metal cation, said salt being present in the solution in amounts of from about 0.05% to about 2% by weight.
 15. A method as defined in claim 14 wherein the polyvalent metal is zinc chloride.
 16. A method as defined in claim 14 wherein the polyvalent metal salt is calcium chloride.
 17. A method as defined in claim 1 wherein there is a second washing treatment with a dilute acid having a dissociation constant of at least about 1 X 10 6, said acid being employed in concentrations of from about 1/2 % to about 3%.
 18. A method as defined in claim 17 wherein the dilute acid is acetic acid.
 19. A method as defined in claim 17 wherein the dilute acid is formic acid.
 20. A method as defined in claim 17 wherein the dilute acid is citric acid.
 21. A method of recovering reusable fibers from mixtures of waste fibers and synthetic, cross-linked polyacrylate resins which comprises: heating a mixture of waste fibers and synthetic, cross-linked polyacrylate resins within the range of from about 85*C. to about 150*C. for a period of from about 1/2 hour to about 2 hours in an aqueous saponifying solution containing from about 1% by weight to about 5% by weight of an alkali metal hydroxide and from about 1% by weight to about 7% by weight of a water-soluble salt containing a monovalent cation, which solution saponifies the synthetic, cross-linked polyacrylate resins and initiates their decomposition or solubilization without undesirably swelling the same; treating the mixture of waste fibers and synthetic, cross-linked, saponified, polyacrylate resins in an aqueous washing solution containing from about 1% by weight to about 7% by weight of a water-soluble salt containing a monovalent cation to remove alkali therefrom; and recovering the reusable fibers from the mixture of waste fibers and decomposed or solubilized synthetic, cross-linked polyacrylate resins. 